1. Field of the Invention
This invention relates to refractory furnace roofs and more particularly to a refractory structure which allows for expansion in an ore reduction furnace roof.
2. Background Art
Large ore reduction furnaces are common in the range of 20 to 40 feet and larger. In furnaces of this size, it is necessary to suspend a refractory roof above the furnace which will enclose the furnace and retain the heat therein. Such roofs typically consist of a number of ceramic blocks or bricks suspended in some way above the furnace.
Inasmuch as the roof is subject to extreme environmental conditions, with temperatures in the range of 2500.degree. F. to 3000.degree. F., and with reactive materials such as sulphur in the atmosphere beneath the roof, the roof will gradually burn away over time. For example, a fifteen inch deep brick might burn down to four inches in only six months or a year depending upon the environment. The environment will vary between furnaces, with the corrosive nature of the environment depending largely upon the sulphur content of the ore being used. Also, since the heat is generally not uniform across the roof, some parts of the roof will burn away at a faster rate than other parts.
Furnace roofs must commonly allow for expansion across the roof (i.e. in the horizontal plane) of 10 percent, or even more. If this were not done, the roof would build up dangerous pressures against the enclosure around its perimeter and would either buckle or break the enclosure. The expansion which must be allowed for includes both thermal expansion, most of which occurs at the beginning of the service life of the bricks, and permanent chemical expansion, due to chemical reactions of the furnace atmosphere with the oxides and bond materials of the roof. The chemical expansion is permanent in that the bricks will maintain that expansion even when they are removed from the furnace environment.
One type of roof which is commonly used to deal with these problems is the panelized roof disclosed in U.S. Pat. No. 3,375,795. Such roofs include multiple brick pairs suspended from a frame, each frame therefore supporting the bricks in a roof panel. Multiple panels are suspended together to form the roof. With small numbers of bricks supported together in this manner, it has been possible to remove and replace those particular parts of the roof which have burned down without replacing those bricks which burned away at a slower rate before it was necessary.
The bricks which have been used in such roofs have been supported by castings which are hooked over the panel frame and which have outwardly directed projections which fit into sockets in the bricks, as shown for example in U.S. Pat. Nos. 3,230,914 and 3,375,795. Forming the bricks with these sockets is however difficult and expensive. Further, the bricks are susceptible to breaking around the socket. Still further, the sockets in the bricks create pockets which have reduced refractory capabilities.
To allow for expansion in such panelized roofs, the panels have been spaced apart when installed by placing various expansion materials between entire panels or rows of bricks. Expansion materials such as wood, corrugated metal plates, or refractory fiber have been used, all of which either burn away or compress to allow for the brick expansion. However, inasmuch as expansion might be 10% or more in severe environments, and since each piece of expansion material has had to accommodate the expansion of numerous bricks, large gaps are required initially for expansion materials large enough to allow for such expansion. Since the expansion materials do not have the refractory characteristics of the bricks, these roofs have thus had large areas with low refractory capability.
The present invention is directed toward overcoming one or more of the problems as set forth above.